Partial combustion or gasification of coal involves reacting the coal at elevated temperatures and possibly elevated pressures with a limited volume of oxygen, the reaction preferably being carried out in the presence of additional agents such as steam, carbon dioxide, or various other materials. Gasification of coal produces a gas, known as synthesis gas, that contains mostly carbon monoxide and hydrogen. Also produced are various liquid and solid materials, such as small particles of ash and carbon commonly known as flyash. This flyash, because it is derived from a "reducing " atmosphere, tends to be different in composition and properties from flyash normally associated with combustion boilers where a fully oxidizing atmosphere is utilized. For example, the flyash from processes for partial combustion of coal may contain elemental iron, sulfides, and deposited carbon, components not normally associated with boiler flyash. In general, the flyash entrained with the gas in partial combustion processes is usually removed from the raw synthesis gas by a combination of cyclones or separators, or a water scrubbing system employing washer coolers, venturi scrubbers, or filters or electrostatic precipitators, or combinations of these systems.
The flyash removed from the synthesis gas may have undesirable properties insofar as its ultimate disposal is concerned. For example, it may be light, friable, dusty and difficult to compact. Because it may contain unsuitable species such as arsenic, selenium, and sulfides, it must be handled with care, and, if it is to be disposed of as land fill, must be in a form which does not release such materials readily to the environment.
In at least one process for the gasification of coal to produce synthesis gas, significant quantities of unreacted impurity matter, variously referred to as char and/or slag, are also produced during combustion or oxidation in the gasification zone. This matter generally segregates in the bottom of the gasification zone, normally in a water bath. Upon separation of the char and/or slag (collectively referred to herein as slag) from the gasification zone, a further solids issue exists, since these materials have undesirable properties which limit options for their utilization or disposal. For example, the slag, as more fully defined in U.S. Ser. No. 813,735, entitled Char Process, filed Dec. 27, 1985, incorporated by reference, may be disposed of as described therein. That solution, however, involves a significant capital cost. The invention addresses the problem of flyash and slag treatment, accomplishing the treatment and providing a novel composition having properties indicating utilities of greater value than mere landfill.